How Thick Should an Asphalt Driveway Be?

The dirt beneath an asphalt driveway can have a big impact on the stability and longevity of the driveway. Once the site is excavated, a compactor machine or hand tamper must be used over the entire surface to compact the dirt down to force out air pockets and underground moisture. If your yard has sandy or clay soil, plan to lay geotextile fabric over the dirt bottom to prevent rocks in the base from sinking into the dirt.

The gravel foundation provides asphalt with the support it needs to endure the daily stress of heavy weight loads. Gravel also provides a flexible buffer that can expand and contract when the ground freezes, preventing cracks and other frost heave damage. The thickness of the gravel base for an asphalt driveway should be at least 8 inches. Plan to install the rocks in 4-inch layers and compact each layer. To prevent the edges of the asphalt from cracking or chipping, make the gravel base 6 inches wider than the asphalt pavement.

The thickness of an asphalt driveway is in part determined by the proportion of liquid asphalt, sand and aggregate in the asphalt mix. Spreading a 3-inch-thick layer of asphalt over the gravel base is thick enough to provide a smooth, solid surface for vehicles. After hot asphalt is spread over the surface, a roller machine compresses the mixture into a dense, uniform layer.

Applying sealer over asphalt will not noticeably raise the level of the asphalt, but it protects the pavement from fading and water damage. The key to successfully sealing asphalt is patience. Unlike other types of pavement, you should wait at least six months for asphalt to set before curing it. Once applied, asphalt sealer lasts for up to six years.